4. Assertion : Quasi- Crystals form when certain molten alloys cool very slowly. Reason : Quasi-crystals have shorts range as well as

a. If both assertion and reason are true and the reason is the correct explanation of the assertion

b. If both assertion and reason are true but reason is not the correct explanation of the assertion

c. If assertion is true but reason is false

d. If the assertion and reason both are false

e. if assertion is false but reason is true.

Ans. b

Explanation : A quasi-crystal is a structure that is ordered but not periodic. If isformed when certain metallic alloy is allowed to cool down slowly from molten state. The range of order is normally short but a few crystals can have long ordered range.